大兴安岭中南段满克头鄂博组正层型剖面火山岩年代学及地球化学特征

Geochronological and geochemical characteristics of orthostratigraphic section volcanic rocks of Manketouebo Formation in south-central sector of Great Xing an Range

满克头鄂博组火山岩年代学及地球化学特征对于大兴安岭中南段大规模火山活动、岩石成因及区域地层对比等方面研究具有重要意义。本文对满克头鄂博组正层型剖面火山岩进行锆石U-Pb年代学及地球化学进行分析。采集的5件测年样品年龄分别为(162.3±1.4)Ma、(163.4±1.3)Ma、(160.9±1.8)Ma、(157.0±1.1)Ma、(162.3±2.2)Ma,形成时代为晚侏罗世。研究区火山岩具高硅、富碱、贫铝钙镁的特点,属准铝质-过铝质高钾钙碱性系列岩石;富集大离子亲石元素Rb、K、Ba及轻稀土元素(LREE),亏损高场强元素Nb、Ta、P、Ti及重稀土元素(HREE),具明显负铕异常。岩浆来源于下地壳岩石的部分熔融,并经历斜长石、磷灰石的分离结晶作用。综合研究区火山岩年代学、地球化学及区域地质资料,认为满克头鄂博组正层型剖面火山岩具A2型花岗岩特征,形成于后碰撞环境,与蒙古—鄂霍茨克洋闭合造山后伸展作用有关。

The geochronological and geochemical characteristics of volcanic rocks of Manketouebo Formation are of great significance for the study of large-scale volcanic activities,petrogenesis and regional stratigraphic correlation in the south-central sector of Great Xing an Range.In this paper,zircon U-Pb geochronology and geochemistry of orthostratigraphic section volcanic rocks of the Manketouebo Formation are analyzed.The ages of the five dating samples collected are(162.3±1.4)Ma,(163.4±1.3)Ma,(160.9±1.8)Ma,(157.0±1.1)Ma,(162.3±2.2)Ma,respectively,belonging to Late Jurassic.The volcanic rocks in the study area are characterized by high silica,alkali enrichment and aluminum,calcium,magnesium deplement,which belong to the paraluminous-peraluminous high potassium-calcium alkaline series.It is enriched in large ion lithophile elements(Rb,K,Ba)and light rare earth elements(LREE),and depleted in high field strength elements(Nb,Ta,P,Ti)and heavy rare earth elements(HREE),with obvious negative europium anomalies.It is suggested that the magma was derived from partial melting of the lower crust,and experienced the fractional crystallization of plagioclase and apatite.Based on the geochronology,geochemistry and regional geological data of volcanic rocks in the area,it is considered that the volcanic rocks in the orthostratigraphic section of the Manketouebo Formation are characterized by A2 type granite and are formed in a post-collision environment,which is related to post-orogenic extension of the Mongolia-Okhotsk ocean closure.